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Recent Developments in the Analysis of the Black Mat Layer and Cosmic Impact at 12.8 ka

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Recent analyses of sediment samples from “black mat” sites in South America and Europe support previous interpretations of an ET impact event that reversed the Late Glacial demise of LGM ice during the Bølling Allerød warming, resulting in a resurgence of ice termed the Younger Dryas (YD) cooling episode. The breakup or impact of a cosmic vehicle at the YD boundary coincides with the onset of a 1-kyr long interval of glacial resurgence, one of the most studied events of the Late Pleistocene. New analytical databases reveal a corpus of data indicating that the cosmic impact was a real event, most possibly a cosmic airburst from Earth's encounter with the Taurid Complex comet or unknown asteroid, an event that led to cosmic fragments exploding interhemispherically over widely dispersed areas, including the northern Andes of Venezuela and the Alps on the Italian/French frontier. While the databases in the two areas differ somewhat, the overall interpretation is that microtextural evidence in weathering rinds and in sands of associated paleosols and glaciofluvial deposits carry undeniable attributes of melted glassy carbon and Fe spherules, planar deformation features, shock-melted and contorted quartz, occasional transition and platinum metals, and brecciated and impacted minerals of diverse lithologies. In concert with other black mat localities in the Western USA, the Netherlands, coastal France, Syria, Central Asia, Peru, Argentina and Mexico, it appears that a widespread cosmic impact by an asteroid or comet is responsible for deposition of the black mat at the onset of the YD glacial event. Whether or not the impact caused a 1-kyr interval of glacial climate depends upon whether or not the Earth had multiple centuries-long episodic encounters with the Taurid Complex or asteroid remnants; impact-related changes in microclimates sustained climatic forcing sufficient to maintain positive mass balances in the reformed ice; and/or inertia in the Atlantic thermohaline circulation system persisted for 1 kyr.
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RECENT DEVELOPMENTS IN THE ANALYSIS OF THE
BLACK MAT LAYER AND COSMIC IMPACT AT 12.8 KA
WILLIAM C. MAHANEY1,2, LESLIE KEISER3, DAVID H. KRINSLEY4, ALLEN WEST5,
RANDY DIRSZOWSKY6, CHRIS C.R. ALLEN7and PEDRO COSTA8,9
1Quaternary Surveys, Thornhill, Ontario, Canada
2Department of Geography, York University, North York, Ontario, Canada
3Department of Geological Sciences, University of Oklahoma, Norman, OK, USA
4Department of Geological Sciences, University of Oregon, Eugene, OR, USA
5GeoScience Consulting, Dewey, Arizona, USA
6Department of Earth Science, Laurentian University, Sudbury, Ontario, Canada
7Department of Biological Sciences, Queen’s University, Belfast, UK
8Centro de Geologia, Faculdade de Ciências da Universidade de Lisboa, Lisboa, Portugal
9Department of Geography, School of the Environment, University of Dundee, Dundee, UK
Mahaney, W.C., Keiser, L., Krinsley, D.H., West, A.,
Dirszowsky, R., Allen, C.C.R. and Costa, P., 2014. Recent
developments in the analysis of the Black Mat Layer and
cosmic impact at 12.8 ka., Geografiska Annaler: Series A,
Physical Geography, 96, 99–111. doi:10.1111/geoa.12033
ABSTRACT. Recent analyses of sediment samples from
“black mat” sites in South America and Europe support
previous interpretations of an ET impact event that reversed
the Late Glacial demise of LGM ice during the Bølling
Allerød warming, resulting in a resurgence of ice termed the
Younger Dryas (YD) cooling episode. The breakup or impact
of a cosmic vehicle at the YD boundary coincides with the
onset of a 1-kyr long interval of glacial resurgence, one of
the most studied events of the Late Pleistocene. New ana-
lytical databases reveal a corpus of data indicating that the
cosmic impact was a real event, most possibly a cosmic
airburst from Earth’s encounter with the Taurid Complex
comet or unknown asteroid, an event that led to cosmic
fragments exploding interhemispherically over widely dis-
persed areas, including the northern Andes of Venezuela and
the Alps on the Italian/French frontier. While the databases
in the two areas differ somewhat, the overall interpretation is
that microtextural evidence in weathering rinds and in sands
of associated paleosols and glaciofluvial deposits carry
undeniable attributes of melted glassy carbon and Fe spher-
ules, planar deformation features, shock-melted and con-
torted quartz, occasional transition and platinum metals, and
brecciated and impacted minerals of diverse lithologies. In
concert with other black mat localities in the Western USA,
the Netherlands, coastal France, Syria, Central Asia, Peru,
Argentina and Mexico, it appears that a widespread cosmic
impact by an asteroid or comet is responsible for deposition
of the black mat at the onset of the YD glacial event.
Whether or not the impact caused a 1-kyr interval of glacial
climate depends upon whether or not the Earth had multiple
centuries-long episodic encounters with the Taurid Complex
or asteroid remnants; impact-related changes in microcli-
mates sustained climatic forcing sufficient to maintain posi-
tive mass balances in the reformed ice; and/or inertia in the
Atlantic thermohaline circulation system persisted for 1 kyr.
Key words: black mat impact, Younger Dryas boundary,
SEM microtextures
Introduction
The black mat beds, originally attributed to a cosmic
impact of 12.8 ka (Firestone et al. 2007a, 2007b),
and found first in the southwest United States have
now been found in other interhemispheric localities
in South America, Europe and Central Asia (Ge
et al. 2009; Mahaney et al. 2010b, 2011a, 2011b,
2013; Bunch et al. 2012; Mahaney and Keiser 2013;
Wittke et al. 2013).While the origin of the sediment
has been disputed vigorously, a key element of the
hypothesis is that the impact coincided with the
onset of a climatic reversal termed the Younger
Dryas (YD). Hence, the YD boundary (YDB) has
been linked to the climatic reversal at the end of the
insolation-induced warming of the Bølling Allerød.
Uncharacteristically, theYD glacial event occurred
even though insolation was still at its peak, appar-
ently unlike nearly all such previous climatic rever-
sals (Firestone et al. 2007a). Still, detractors argue
that similar climatic anomalies are normal at the end
of glacial periods (Broecker et al. 2010) and that
some black mat beds may be due to terrestrial
processes such as redox fluctuations in aquifers
(Quade et al. 1998), although these arguments do
not preclude an impact. Black mat sediment has
been dated to within a few hundred years of theYDB
(Mahaney et al. 2010b), and arguments have been
made that the black mat and the YD are merely
coincidental and that a single cosmic impact would
be unable to generate climatic forcing sufficient to
change the mass balance of glaciers worldwide for
© 2013 Swedish Society for Anthropology and Geography
DOI:10.1111/geoa.12033 99
up to 1 kyr. Recent data supporting a previously
fragmented cometary vehicle (Comet Encke) break-
ing up further over southern Canada at the time
frame of the black mat (Napier 2010) may well have
spun off fragments radially which generated air-
bursts over various locales, but some (Higgins et al.
2011) still favor an asteroid impact.
Recent analyses of black mat beds in the north-
western Venezuelan Andes (location Fig. 1a, stra-
tigraphy Fig. 1b), to be described here, show
conclusive micrographic and chemical evidence of
the existence of aerodynamically quenched quartz
and chemical signatures that could only be pro-
duced by an ET airburst/impact. Add to this the
presence of glassy carbon, Fe-rich grains, planar
deformation features, occasional platinum metals
and carbon welded to partially melted quartz in
sediment, associated with and overrun by YD ice,
and all this evidence supports an extremely high-
temperature event caused by cosmic fragments that
produced the YDB layers in South America and in
the Alps.
Examination of Late Glacial (LG) and YD
moraines and mass-wasted debris in the Cottian
Alps of France and Italy (location Fig. 2a;
moraines, Fig. 2b) shows that ice recession during
the Bølling-Allerød chronozones was interrupted
by the advance of YD ice, followed by moraine
emplacement (Mahaney and Keiser 2013). At the
sites examined, the impact layer is atypical to that
found elsewhere, due perhaps to active glacial and
glaciofluvial processes in play. Instead, the impact
record at these sites is archived in weathering rinds
(Fig. 2c) and in paleosol Ah epipedons (Fig. 2d), the
latter similar in kind to signatures described else-
where by Courty and Federoff (2010), both consid-
ered as resulting from an airburst. Weathering rind
thickness has been used for relative age determina-
tion in postglacial deposit sequences (Sharp 1969;
Birkeland 1973; Mahaney 1978; Chinn 1981;
Ricker et al. 1993; Dixon et al. 2002; Laustela et al.
2003; Sak et al. 2004), for microweathering analy-
sis (Oguchi 2004; Nicholson 2009; Mahaney et al.,
2012a and 2012b), and for isotopic dating of pen-
etrating fluids (Pelt et al. 2003), but to date, evi-
dence of cosmic impacts in weathering rinds has not
been encountered by workers seeking to establish
weathering histories and relative ages of glacial
deposits. A preliminary search of rock rinds in LG
recessional moraines (Guil3 =G3 site, n=50) and
mass-wasted debris sheets (Viso9 =V9; n=50) of
the Western Alps (Fig. 1) produced evidence of a
cosmic impact (Mahaney and Keiser 2013). Cross
analysis of rinds in pebbles embedded in younger
YD-aged moraine surfaces (n=100) did not
produce grains with similar melted microtextures
which indicate that the YD moraines postdate a
possible airburst.
Regional geologies
The Mucuñuque Catchment (Fig. 1a) drains the
northwestern slope of the cordillera Sierra de Santo
Domingo in the eastern cordillera of the Mérida
Andes (northwestern Venezuelan Andes). As one
of the prominent drainages in the area, it contains a
record of LG stillstand of retreating ice that was
overrun with push moraine deposited during the
YD, along with outwash that was emplaced during
withdrawal of the glacier (Mahaney et al. 2008).
Oriented SW–NE, the Mérida Andes extend from
the Venezuelan–Colombian border toward the Car-
ibbean Coast, constituting a 100-km-wide moun-
tain belt with summits reaching to 5000 m a.s.l. As
a consequence of plate collision (Audemard and
Audemard 2002), the mountains formed during an
orogeny that began in the Late Miocene. Both the
Sierra de Santo Domingo and the Mucuñuque
Catchment, located on the northeastern limb of the
Boconó Fault, are floored with Precambrian
bedrock of gneiss and granite of the Iglesias Group
(Schubert 1970).
The SE–NW-oriented Mucuñuque Catchment is
a fault-controlled glacially carved valley, which
descends from elevations above 4200 m on the
western slopes of Pico Mifés (4600 m a.s.l.) and
Pico Mucuñuque (4672 m a.s.l.). Debouching into
Lago Mucubaji (c. 3600 m a.s.l.), the Mucuñuque
Valley drains across the MUM7 and MUM7B
sites (Mahaney et al. 2010b) into the Rio Santo
Domingo, eventually emptying into the Orinoco
Basin. Upstream of LG recessional moraines
(Mahaney and Kalm 1996; Mahaney et al. 2008),
investigations reveal surface moraine (site MUM7)
and outwash fans (site MUM7B), the latter burying
alluvial peat dated to within the YDB window. The
outwash documents both the advance and retreat
of YD-aged ice (see Mahaney et al. 2008 for
Fig. 1 (opposite page). (a) Location of MUM7B, northwestern Andes; (b) stratigraphy of the site showing the Fe/Mn encrusted bed.
Figs 1A and 1B from Mahaney, Krinsley and Kalm, 2011b.
WILLIAM C. MAHANEY ET AL.
© 2013 Swedish Society for Anthropology and Geography
100
(a) (b)
MUM7B
Glaciofluvial pebbly sand, Mn rich
MUM7B
RECENT DEVELOPMENTS IN THE ANALYSIS OF THE BLACK MAT LAYER AND COSMIC IMPACT AT 12.8 KA
© 2013 Swedish Society for Anthropology and Geography 101
stratigraphy), and the MUM7B section (Fig. 1b),
situated at 3800 m a.s.l., contains the YDB black
mat sediment with aerodynamically shaped grains
described in this report.
The two deposits investigated in the Alps are
located at 2300 m a.s.l. (site V9, Upper Po River,
Italy) and 2450 m a.s.l. (site G3, Guil River, France)
(Fig. 2a). The V9 site is in the outermost lobe of the
Traversette Rockfall of LG age (Mahaney et al.
2010a), abutting an inner recessional moraine of
LG age. The upper G3 site is located by hand-set
GPS at 4952235N; 32345383E, on the youngest LG
moraine, partially overrun by a YD moraine. The
Guil River catchment in the Western Alps (Fig. 1) is
a linear fault-controlled glacial basin with headwa-
ters on the western slopes of Mt Viso(3841 m a.s.l.),
sourced from the France/Italy border area. While
active glacial erosion and postglacial mass wasting
is evident on both the north- and south-facing valley
slopes, recessional moraines are non-existent below
2400 m a.s.l., which clearly indicates that retreat of
LG (Würm/Weichselian) Guil ice from the Durance
valley (where it previously joined the larger
Durance Glacier) was rapid. Hence, recessional
stillstands of LG ice are not recorded in the surface
record, if they occurred at all. Soils on the valley
floor and sides are in alluvial and mass-wasted
deposits and all are thin Entisols (Cryorthents
mainly; National Soil Survey Center (NSSC) 1995).
Some carbon in the melted pebble clasts embedded
in LG moraines may have been sourced from sparse
vegetation and associated thin Entisols (NSSC
1995; Birkeland 1999) of the alpine grassland.
Encrustation of carbon onto rinds would have
occurred when an impact-related, high-temperature
cloud, similar in kind to the Andean event described
above, descended upon the area producing a wild-
fire conflagration that destroyed most life, including
plants in what was likely a wet tundra in its early
developing seral stage (Mahaney and Keiser 2013).
Prominent recessional moraines (Fig. 2b) are
found only at the 2400 m a.s.l. contour within the
(a) (b)
(c) (d)
Fig. 2. (a) Location of the black mat sites, western Alps of France and Italy; (b) Late Glacial andYounger Dryas moraines, upper Guil
River, France; (c) Macrophotograph of clast rinds, sites G3 and V9 (westernAlps) carrying impacted signatures; (d) paleosol profiles
G3 and V9 showing surface horizons carrying melted minerals. Figs. 2a, 2b and 2d from Mahaney et al., 2013.
WILLIAM C. MAHANEY ET AL.
© 2013 Swedish Society for Anthropology and Geography
102
Guil drainage, located approximately 1 km from
the drainage divide at 3000 m a.s.l. The innermost
LG recessional moraines, partially overrun by a
glacial readvance interpreted to be the YD, exhibit
similar weathering characteristics to the LG but
lack any melted characteristics which might infer a
cosmic airburst. Thus, since paleosol development
and weathering properties of coarse clastic debris
on LG and YD deposits are similar, they must have
an age separation of mere centuries to at most a
millennium. Above the LG/YD moraine elevations,
steep slopes cross a bedrock bar leading into a
prominent cirque (below the Col de la Traversette
3000 m a.s.l.; Mahaney 2008), the latter floored
with Little Ice Age rockfall and talus cover, all
lacking ground moraine. While LG ice may have
receded into the Traversette cirque prior to the YD,
it is unequivocal that the YD ice advanced to
2450 m a.s.l. at a later date, overrunning the upper
LG recessional moraine.
Methods
Deposits for both areas were mapped from air
photos, and sites selected on the basis of representa-
tive deposit and soil expression. Deposits, including
MUM7B (Mahaney et al. 2010b, 2011a, 2011b),
were investigated for LG stratigraphy and radiocar-
bon controls. The Western Alps sites were similarly
studied for differentiation of LG andYD weathering
characteristics and paleosol properties. Both theYD
and LG deposits were sampled for rinds, and counts
with corresponding soil/stratigraphic pits estab-
lished in each case.
At the Andean site (Fig. 1a), deposit stratigraphy
was established in conjunction with a moraine stack
of deposits at site MUM7 (Mahaney et al. 2008), the
attempt being to add radiocarbon control to the
withdrawal ofYD ice and emplacement of outwash
forming a cap on the stratigraphic sequence. In the
western Alps, pebbles of uniform lithology were
collected from moraine and rockfall surfaces,
cracked with a rock hammer, after which exposed
rinds (Fig. 2c) were measured to the nearest mm
perpendicular to the pebble surface inward to the
fresh lithic core. Because rinds indicate the degree
to which Fe-bearing minerals have oxidized and
discolored the outer periphery of clasts, the rind
thickness is used to estimate time since deposition
(Birkeland 1973; Mahaney 1990). Since most
researchers measure only the maximum thickness
of discoloration/alteration, neglecting the irregular
rind thickness observed in most specimens, meas-
urements reported here were made for both
maximum and minimum rind dimensions on each
clast (Mahaney 1990). Normally the maximum rind
is in the clast surface in contact with the subaerial
atmosphere and biosphere, the minimum rind
in contact with the underlying soil/paleosol.
Maximum rinds are defined from the maximum
thickness measured in the outer surfaces of a popu-
lation of 50 pebbles of similar lithology at each site.
Minimum rind measurements are determined from
minimum thickness measurements for the same
population of 50 specimens. The populations of
maximum and minimum rind thicknesses, sub-
jected to a means test, yield a mean maximum value
representative of maximum weathering at a site and
mean minimum value representing the lesser pen-
etration of reacting fluids. In this case, however, rind
development may have been accelerated by a high
temperature conflagration that fractured coarse
clastic sediment, producing melted streams of
olivine, pyroxene, amphibole and quartz that pen-
etrated inward, post-impact weathering in some
cases penetrating to the internal fresh rock core.
Selected grains from rind subsamples (G3 and
V9) were mounted on stubs for analysis by normal
scanning electron microscopy (SEM), using sec-
ondary electrons (SE), backscattered electrons and
energy-dispersive spectrometry (EDS), following
methods outlined by Mahaney (2002). The Andean
grains were subsampled and separated with a Nd
magnet, the recovered Fe spherules subjected to a
similar analysis. Because carbon is important in the
analysis, samples were coated with gold paladium
(Vortisch et al. 1987; Mahaney 2002). Both SEM
imagery and x-ray microanalysis (EDS) were
obtained at accelerating voltages of 20 keV.
Results
The black mat
The black mat beds thus described from various
locations in North and South America, Europe, and
Central Asia are normally 2–3 cm thick C-rich or
C+Fe+Mn-rich layers found within lacustrine or
bog sections or in marginal glaciofluvial sections
from Greenland. The Andean locality inVenezuela,
described by Mahaney et al. (2010b, 2011a, 2011b),
consists of a glaciofluvial bed of pebbly sand having
a composition of felsic gneiss and granite, fine
grained glassy and opaque C, plus Fe-rich spherules
welded to quartz and other minerals. Quartz, in
particular, appears as contorted and partially melted
material. The black mat beds, dated to 12.8 ±0.2
RECENT DEVELOPMENTS IN THE ANALYSIS OF THE BLACK MAT LAYER AND COSMIC IMPACT AT 12.8 KA
© 2013 Swedish Society for Anthropology and Geography 103
calibrated ka, have yielded aerodynamically modi-
fied Fe spherules that most likely formed in a local
airburst, resulting from a fragmented asteroid or
comet. As shown with the Andean example, the
burnt layer material represented by a high-carbon
signature was first thought to result from a lightning
strike and resultant fire (Mahaney et al. 2008),
although the conflagration temperature in a wet
Andean tundra undergoing first or second stage
succession vegetation growth would not have been
of sufficiently high temperature to melt quartz.
Also, brushfire temperatures do not produce a tem-
perature high enough to produce glassy C-rich
spherules firmly welded to mineral surfaces as
occurred with the Andean example (Mahaney et al.
2010b, 2011a, 2011b).
Despite the absence in the Alps of the typical
black mat bed, weathering rind archives of LG age
were found that consisted of associated carbon
welded onto pyroxene and quartz, dislocated and
partially melted and shocked pyroxene, olivine,
amphibole and quartz species, and thick breccia
within the outermost 1 mm of mineral surfaces.
Interpreted as the result of the YDB impact, this is
a new corpus of data (Mahaney and Keiser 2013)
of the black mat event not previously encountered
by workers researching LG/YD glacial sequences.
The rind archives lead to a testable hypothesis fol-
lowing from previously reported data (Mahaney
et al. 2011a, 2011b). The high-carbon layer in the
rind material of the Alps is similar to burnt material
correlated by Mahaney et al. (2010b) with black
mat beds described elsewhere in North and South
America, Europe and Central Asia but with some
differences, as described below. For one, the Alps
impact was of sufficient intensity to create thick
(1 mm) breccia layers in coarse clasts and to open
wide fractures that filled with melted quartz,
pyroxene, olivine and plagioclase, all part of the
country rock lithology, as well as allochthonous
materials, including rutile and zircon. For another,
small amounts of Tc and Pt were detected by EDS
analyses, although the presence must be confirmed
and the origin is unclear. The presence of Tc, in
particular, found from chemical mapping of grains,
may well be either a false positive or residue from
the Chernobyl meltdown of 1986. Along with
impacted clast rinds, Ah horizons in associated
paleosols contain not only similar impacted relict
grains produced by the cosmic impact, they also
contain Fe spherules similar to those recovered
from the Andean site. All the more important
perhaps is the microbiological record in the Ah
horizon of one paleosol (G3; Fig. 2d) that yielded a
density gradient gel electrophoresis profile dissimi-
lar to genetic profiles obtained from lower horizons
in other LG profiles and all horizons in two YD
profiles within the same catchment (Mahaney et al.
2013). While yet to be proven with a greater popu-
lation of samples, this microbiological perturbation
may result from very small differences in the level
of rare isotopes, including radioactive isotopes,
released upon impact exerting selective pressure on
the microbial population (Melott and Thomas,
http://arxiv.org/ftp /arxiv/papers /1102/1102. 2830
.pdf, 18-Nov-13; Rainey et al. 2005).
The analysis of cosmic-impacted grains in Ah
horizons of two paleosols under discussion here
requires a comparison with black mat grains
described in the Northern Andes (Mahaney et al.
2008, 2010b). Specific grain microtextures include
intense brecciation and internal fracture patterns in
both sample suites with a degree of brecciation and
fracturing less intense than in the Andean samples.
In my opinion (WCM), brecciation in weathering
rinds is a unique feature never seen in the thou-
sands of rinds measured over some 45 yr on all
continents. The brecciation may be a function
of both impact compression and heating, with
incoming high speed particulate matter releasing
enormous kinetic energy capable of producing dis-
ruption of mineral fabric to a rind depth of
1000 μm with crack propagation reaching even
deeper into the rind body in the case of the Alps
samples. Microfractures are oriented, both parallel
and normal to the surface, and the pattern is related
to variable impact energy and resulting energy
cone vectors. Microfabric analyses of the Alps
samples reported here are similar to those in
Mahaney et al. (2011b).
The criteria for the YD impact is similar to evi-
dence used to prove the KPg impact (formerly
K/T) (Hildebrand 1993), with the exception that
the G3 Alps locality is in metamorphic terrane
which was under glacier recession at the time of
impact. The impact evidence is in pebble size clasts
found embedded in the inner LG recessional
moraine surface located in front of a doublet cross-
cutting moraine of presumed YD age. While 14C
dates are not available for the LG at the G3 site and
YD moraines (sites G1 and G2), the outer YD
moraine buries part of the inner LG recessional,
clearly the result of a glacial readvance. The lack of
lakes/bogs in LG deposits suitable for coring
makes it impossible to find sites with resident
impact beds still intact, so that clasts on LG
WILLIAM C. MAHANEY ET AL.
© 2013 Swedish Society for Anthropology and Geography
104
moraine and rockfall deposits and sands in the
surface paleosol epipedons are the only reposito-
ries of the cosmic impact discovered to date in
these two catchments of the French and Italian
Alps.
Andean samples
The glassy and opaque carbon and Fe spherules
welded to coarse clastic sediment in the Andean
site are shown in Fig. 3(a, b). Mixed within these
spherules are contorted, partially melted quartz
grains, implying temperatures >1730°C (Fig. 3c),
mats with quartz welded to carbon, and very coarse
sands and granules, all fractured and with many
carrying brecciated surfaces (Fig. 3b). The sand
fraction in numerous subsamples collected from
the black mat bed yielded a magnetic fraction with
aerodynamically modified Fe spherules (Fig. 3d)
with oxide wt% values (Table 1) for the MUM7B
spherules that, although somewhat lower than
mean concentrations for other aerodynamically
modified grains, closely correlate with widely
accepted impact material and previously analyzed
YDB material (Bunch et al. 2012; Israde-Alcántara
et al. 2012). There is minor overlap of the MUM7B
sediment with cosmic material but the lack of
MgO enrichment makes them dissimilar to 95% of
(a) (b)
(c) (d)
Fig. 3. (a) Light micrograph of impacted sand/spherules in the MUM7B bed northwestern Andes; (b) carbon encrusted spherules on
felsic gneissic granule; (c) impacted and partially melted quartz-rich, elongated spherule; (d) melted Fe-spherule with remaglypt
aerodynamically shaped microtexture. Fig. 3a from Mahaney et al., 2010b.
RECENT DEVELOPMENTS IN THE ANALYSIS OF THE BLACK MAT LAYER AND COSMIC IMPACT AT 12.8 KA
© 2013 Swedish Society for Anthropology and Geography 105
glassy cosmic spherules discussed in Bunch et al.
(2012). These high-Fe Andean spherules are not
volcanic in origin, as demonstrated by Mahaney
et al. (2013), but all recovered spherules plot
within the acknowledged characteristics Evidence
was provided previously of terrestrial impact mate-
rials, including documented spherules, ejecta and
tektites from 12 craters and tektite strewnfields
(n=1000), including the Chicxulub crater
(Hildebrand 1993), Chesapeake Bay crater, Tun-
guska, Australasian tektite field, Lake Bosumtwi
crater, Ries crater, and more (Bunch et al. 2012).
Alps samples
Within the Alps samples from G3 and V9, there are
impacted grains, similar to the Andes samples in
surface microtexture characteristics, but with
different lithologies. They yield fewer Fe and C
spherules, but have a greater quantity of near-
micron-size grains welded to mineral fabric, as
shown in one G3 sample (Fig. 4a). Small particulate
matter of largely pyroxene composition, encrusted
with carbon (dark tonal contrast is C, light Fe), is
frequently found within the outer 1000 μm rind
thickness. Carbon mats with opaque thick layers,
and soot from wildfires seen elsewhere (Stich et al.
2008), are similar to the specimen covering a parti-
cle of metabasalt, all welded to the grain surface.
The outer rind area shown in Fig. 4(b) is filled with
contorted and shocked pyroxene and quartz, many
grains of which are the product of immense shock.
Some disrupted grain surfaces register as Cl on the
EDS, suggesting they might be chloride ion sites in
silicate and aluminosilicate glass from an airburst
(Stebbins and Du 2002).
A second group of rind samples from site V9 in
the upper Po River valley reveal similar fragmental
breccia, melted pyroxene, and partially melted and
contorted quartz (Fig. 5a). One EDS spot analysis
(Fig. 5b), indicates the presence of Tc and Bi in a
melted pyroxene spherule, the former element
rarely found in nature, so that proof of its presence
would require a wider search with high-resolution
EDS. Bismuth, common in pyroxene, is unrelated
to a cosmic airburst.
Table 1. Chemistry of near full scale silt size spherules in Figure 3, C and D frames of the MUM7B section, northwestern Andes.
Sample Elements
O Al Si K Ca Ti Fe Mn
C 41.82 6.66 11.23 0.39 0.90 1.21 37.78 –
D 49.82 8.49 12.25 2.58 – 12.73 13.47 0.66
(a) (b)
Fig. 4. (a) Contorted and welded pyroxene, plagioclase and quartz grains in two subsamples of the G3 rind, western Alps; (b) melted
lithologic mix in the outer G3 Rind, western Alps.
WILLIAM C. MAHANEY ET AL.
© 2013 Swedish Society for Anthropology and Geography
106
Discussion
The G3 site, located on the inner recessional
moraine in the upper Guil River valley, is situated
such that it received sufficient heat required to melt
outer clast surfaces, presumably from the full force
of a cosmic airburst covering an indeterminate area
of the French and Italian Alps. The exact time frame
is unknown due to a lack of 14C controls, but the LG
age of the G3 deposit is undeniably correlated with
the warming event of the Bølling-Allerød climatic
forcing that led to the recession of the Guil Glacier,
a feeder system into the massive Durance Glacier.
Near the end of the last glaciation, ice was in the
final stage of retreat in the upper Guil Valley close to
Mt Viso (3841 m a.s.l.) with the main ice sheet
separated into two glaciers, one to the north retreat-
ing into the Traversette Cirque and the other into an
unnamed cirque to the south below the summit of
Mt. Viso. It is impossible to reconstruct the posi-
tions of these two retreating glaciers after 12.8 ka,
but it is possible to establish that the retreating
glacier occupied a stillstand position prior to the
cosmic impact and established a moraine system
now partly eroded, principally by outwash from
later established YD ice. What is certain is that a
glacial resurgence, presumably during the YD
cooling interval, emplaced a crosscutting end
moraine that partially buried the LG moraine creat-
ing a small tarn, now filled with coarse clastic debris
from talus and debris flows. Close analysis of rinds
at the YD and LG sites indicates the impact signa-
ture is present only in the LG clasts and paleosol Ah
horizon, with such signatures lacking at the YD
sites. Because the LG deposit is within the time
frame of the black mat sites established elsewhere,
and also because the normal black mat grain signa-
ture is present within the rinds and the surface
paleosol epipedon, it is reasonable to assume that
this evidence resulted from the 12.8 ka impact.
There is no other proposed impact event that falls
into the LG time frame.
The V9 site in the old lobe of the Traversette
Rockfall in the upper Po River valley is dated
similarly to the LG sites in the upper Guil River.
No 14C dates are available for the rockfall, but the
deposit is clearly a two-stage system, as originally
described by Polybius, a Greek general in antiq-
uity, who followed the invasion route of the Punic
Army in 160 BC (Mahaney et al. 2010a). We
cannot conclusively correlate the rockfall with the
LG, but the presence of a cosmic signature, both in
rock rinds and in the Ah horizon of the paleosol
epipedon of the rockfall deposit, suggests the mass
wasting event occurred during the LG.
Following the YDB event, the climatic situation
reversed with renewed cooling, the onset of a posi-
tive glacier mass balance, and the advance of YD
ice. The glacial advance left a wealth of glacial
geomorphic and sedimentological evidence, but
lacks any cosmic signature, indicating that it post-
dates the event. The LG stillstand recessional
moraines provide coarse clastic debris that acted as
host material for weathering rind development, part
of which contains evidence of a cosmic impact and
resulting wildfire that created soot welded to heated
and melted materials. Presumably, the impact was
the progenitor of theYD climatic reversal, the latest
event in the LG record (Ralska-Jasiewiczowa et al.
2001; Gibbard 2004). The YD onset begins at the
upper end of a warming trend that began at 14.7 ka
(Van der Hammen and Hooghiemstra 1995; Teller
et al. 2002; Lowe et al. 2008) with maximum
cooling beginning at 12.8 ka. The hypothesis that a
cosmic impact could have generated theYD reversal
is still hotly debated in the literature (Haynes 2008;
Pinter and Ishman 2008; Ge et al. 2009; Kennett
Fig. 5. (a) Brecciated outer rind area of V9 with melted quartz
upper left and identified possible transition metal (Tc) composi-
tion overlapping with Bi (from Mahaney and Keiser 2013); (b)
EDS of (a) (from Mahaney and Keiser 2013 and Mahaney et al.,
2013).
RECENT DEVELOPMENTS IN THE ANALYSIS OF THE BLACK MAT LAYER AND COSMIC IMPACT AT 12.8 KA
© 2013 Swedish Society for Anthropology and Geography 107
et al. 2009; Kennett et al., 2007). Recent critical
reviews of the YD event by Van der Hammen and
Van Geel (2008) and Broecker et al. (2010) argue,
respectively, that charcoal in paleosols of the
Allerød–YD transition were not caused by impact,
and that the impact event, by itself, could not have
caused a glacial advance lasting 1 kyr. The evidence
reported here conclusively contradicts alternative
hypotheses for the onset of the YD glacial advance,
with the most conclusive evidence coming from
aerodynamically modified Fe spherules and micro-
spherules, melted and contorted quartz and other
lithologies, and carbon mats welded to various
minerals.
The presence of technetium, a rare radioactive
byproduct of uranium fission, could be a product of
a postulated large scale, if momentary disruption of
the atmosphere, sufficient to allow a cosmic ray
burst. Technetium (AN 43) occupies a position in
the periodic table between Mo (AN 42) and Re (44),
the latter platinum element recently detected in
melted pyroxene in site G3 weathered rind sedi-
ment. As a product of atomic bomb blasts
(Yoshihara 2006), and its presence in carbon stars
(Bernatowicz et al. 2006), Tc might be an undiscov-
ered by-product of a bolide or comet impact. Alter-
natively, it may be an air-influxed contaminant from
nuclear reactors (Istok et al. 2004), i.e. Chernobyl,
or a false positive, as indicated previously. Tc was
found in only one occurrence out of hundreds of
grains analyzed, indicating it is not widespread.
More work is needed to confirm its presence and
determine its origin.
Conclusions
Impacted black mat sediment is present in the
Western Alps, where it is found in surface clast rinds
embedded in LG moraine/rockfall sediment and in
paleosols of the western Alps near Mt Viso on the
French/Italian border. The same black mat deposits
are also found in the Andes, displaying glassy Fe/C-
rich spherules and the presence of high fractures and
clast brecciation, complete with melted/quenched
and aerodynamically shaped microtextures. The
evidence at both sites is consistent with the sediment
being the product of cosmic airburst/impact. The
relationship with YD till is indisputable, and 14C
dates associated with the black mat beds in the
Andes, place the impact squarely within the YDB
window.
Evidence of cosmic impact in the Western Alps
occurs both in weathering rinds and within surface
paleosol Ah horizons, all of LG age. We report
finding highly fractured and brecciated weathering
rinds, complete with multiple impact-related chan-
nels filled with melted and contorted grains. These
formed from a highly volatile and viscous mass of
molten material, now welded together into chains
of fused grains and coated with thick opaque
carbon, occasionally revealing the presence of Al
plus Cl considered to be impact-produced glass.
Although the relationship between the YDB and
the YD is still under discussion, it is clear that the
black mat extends to the European Alps, and it is
also clear that the evidence for it is found both in
weathering rinds and in resident grains of Ah paleo-
sol profiles. At the time of impact theseAh horizons
were likely C or Cox (ox =oxidized) soil horizons
undergoing the initial stage of weathering following
deglaciation. This is the first report of black mat
archival evidence recovered from weathering rinds
and from surface paleosol horizons. The spatial
evidence of deposit juxtaposition (the Alps) and
superposition (the Andes), strongly indicates cause
and effect regarding the black mat as related to the
YD. The geomorphological situation in both locali-
ties is such that ice withdrawal during the Bølling
Allerød was interrupted by a glacial resurgence in
two widely separated interhemispheric areas, both
with indisputable evidence of a cosmic impact. In
the Andes,YDB dated beds were overrun by YD ice
while in the Alps cosmic impacted beds were par-
tially overrun and buried byYD moraines. It would
seem prudent for other workers to analyze rinds and
paleosols in similar venues in both areas to add to
the database presented here.
Acknowledgements
This research was funded by the Garage Institute of
Quaternary Surveys, Toronto. We are indebted to
Gary Stowe and Jeremy Jernigan for assistance with
the SEM/EDS analyses. We gratefully acknowledge
support from the Petroleum Engineering Depart-
ment, University of Oklahoma, Norman. We greatly
appreciate critical reviews from the two anonymous
reviewers.
William C. Mahaney, Quaternary Surveys, 26 Thornhill Ave.,
Thornhill, Ontario, Canada L4J 1J4 and Department of
Geography, York University, North York, Ontario, Canada
M3J 1P3
E-mail: arkose@rogers.com
Leslie Keiser, Department of Geological Sciences, Univer-
sity of Oklahoma, Norman, OK 73019-1009, USA
E-mail: lkeiser@ou.edu
WILLIAM C. MAHANEY ET AL.
© 2013 Swedish Society for Anthropology and Geography
108
David H. Krinsley, Department of Geological Sciences, Uni-
versity of Oregon, Eugene, OR 97403-1272, USA
E-mail: krinsley@uoregon.edu
Allen West, GeoScience Consulting, Dewey, AZ 86327, USA
E-mail: allen7633@aol.com
Randy Dirszowsky, Department of Earth Science, Lauren-
tian University, Sudbury, Ontario, Canada P3E 2C6
E-mail: rdirszowsky@laurentian.ca
Chris C.R. Allen, Department of Biological Sciences,
Queen’s University, Belfast, N. Ireland, UK.
E-mail: c.allen@qub.ac.uk
Pedro Costa, Centro de Geologia, Faculdade de Ciências da
Universidade de Lisboa, Edifício C6, Campo Grande, 1749-
016 Lisboa, Portugal, and Department of Geography,
School of the Environment, University of Dundee, Nether-
gate, Dundee DD1 4HN, UK
E-mail: ppcosta@fc.ul.pt
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Manuscript received 21 Jun., 2013; revised and accepted 25
Oct., 2013
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© 2013 Swedish Society for Anthropology and Geography 111
... Indeed, recent evidence from the last few years from three independent research groups has revealed a platinum anomaly that extends at least across North America, Greenland and North-West Europe, coeval with other evidence for a cosmic impact, including impact spherules, magnetic grains and nano diamonds [24][25][26]. Although disputed by several prominent and vocal research groups, their counter-arguments are generally weak to non-existent while evidence from independent research groups continues to accumulate [27][28][29][30][31][32][33][34]. ...
... Black mats at four of the sites (Cuitzeo core, Acambay core, Chapala core, and Tocuila trench) display evidence of a cosmic impact event, indicated by high-temperature, melted microspherules within the black mat layer. The microspherules, charcoal, and soot are consistent with the hypothesis that the YDB impact event caused sudden wildfires that consumed the local biomass, as in other YDB sites in seven countries across three continents (LeCompte et al. 2012;Mahaney et al. 2014;Wittke et al. 2013). The depth to the YDB layer in the studied lakes varies widely, because the local sedimentation rates vary, with the YD at 2.80, 3.87, and 1.90 m at Cuitzeo core, Acambay core, and Tocuila trench respectively. ...
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The Younger Dryas interval (YD) was a period of widespread, abrupt climate change that occurred between 12,900 and 11,700 cal yr BP (10,900–10,000 ¹⁴C BP). Many sites in the Northern Hemisphere preserve a sedimentary record across the onset of the YD interval, including sites investigated in sedimentary basins located in central Mexico (Chapala, Cuitzeo, Acambay), the Basin of Mexico (Tocuila), and northern Mexico (El Cedral). Deposits consist of lacustrine or marginal lake sediments that were deposited during the Pleistocene and the Holocene. At the Tocuila and Acambay sites, Pleistocene fossil vertebrate assemblages, mainly mammoths (Mammuthus columbi), are found in association with a distinctive organic layer, sometimes called the black mat that formed during the YD. At the Chapala, Cuitzeo, Acambay, and Tocuila sites the black mats contain a suite of distinctive microscopic and mineralogical signatures and are accompanied by a sharp change in the depositional environments as supported by diatom and pollen studies reported here. The signatures include magnetic, Fe-rich microspherules, silica melted droplets with aerodynamic shapes (tektites), large amounts of charcoal, and sometimes nanodiamonds (Cuitzeo), all of which were deposited at the onset of the YD. The geochemistry of the microspherules indicates that they are not anthropogenic, authigenic or of cosmic or volcanic origin, and instead, were produced by melting and quenching of terrestrial sediments. Here, we present the stratigraphy at five field sites, the analyses of magnetic microspherules, including major element composition and scanning electron microscopy images. All of these materials are associated with charcoal and soot, which are distinctive stratigraphic markers for the YD layer at several sites in Mexico.
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The enigmatic black mat sediment complex in the northern Andes, previously considered the product of a high-grade lightning strike and low grade brush fire, has been upgraded recently to a conflagration resulting from incoming asteroid/comet impact over the Laurentide Ice Sheet at approximately 12.9 ka. Previous evidence from the black mat beds of disrupted quartz and orthoclase grains and intense firing from incoming C-rich ejecta is further supported by new SEM/EDS and FIB analyses of fine grain silt and clay spherules (10-∼2 μm dia.) of C, Fe and Mn composition, a mixed material of partly ejecta and partly country rock. Because the environment at the time of ejecta impact was in the initial stage of seral vegetative development as wet tundra, part of the clay/organic balls, classic 'house of cards' form, which constitute a portion of the sediment complex, may be of cosmic origin. Evidence of cyanobacteria and fungal filaments on and within grain coatings are probably post depositional and therefore of terrestrial origin.
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Weathering rinds on surface boulders of the Torlesse Supergroup sandstones of New Zealand thicken with time. Weathering-rind thicknesses provide a means of determining the age of surfaces where age (years) = 1030 R1.24 and R is modal rind thickness (mm) of about 50 boulders on the surface of the deposit. Rind thickness measurements on moraines in the Upper Waimakariri catchment help to establish a Holocene glacial chronology for the area. Times of cirque glacier advance are 0 to 430, 1000 to 2500, 4000, and 7600 to 9500yr BP. -from Author Ministry of Works and Development P.O. Box 1479, Christchurch, New Zealand.
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Data from several relative age-dating methods were collected on rock glacier debris mantles to test the usefulness of each in assigning a relative age to various parts of the mantles. Lichens, rock weathering, and soils provide the best information on age. No single method is adequate to differentiate all the deposits, most of which have been formed within the past 20,000 to 30,000 years. Each method has an ages to the Neoglacial deposits. The Neoglacial- of each method differs. Lichen data, specifically Rhizocarpon geographicum s.l. size, percentage of total lichen cover, and species composition provide the best information for assigning ages to the Neoglacial deposits. The Neoglacial-Pinedale break is recognized from a much thicker surface deposit of loess, thicker and more common rock weathering rinds, and greater soil development on Pinedale deposits relative to early Neoglacial deposits. The Pinedale-Bull Lake break was not satisfactorily recognized in many places. Where exposures are present, however, the granitic rocks in the weathered zone in Pinedale deposits are fresh whereas a substantial number of those in Bull Lake deposits are grusified.